Adjustable tap or the like



Ap 7, 1.942. c. c. WINTER ADJUSTABLE TAP OR THE LIKE Filed Feb. 13, 1941 I Iwvenifoz Ckarles C. M 4

Patented Apr. 7, 1942 ADJUSTABLE TAP OR THE LIKE Charles C. Winter, Wrentham, Mass, assignor to Winter Brothers Company, Wrentham, Mass.,- a corporation of Michigan Application February 13, 1941 Serial No. 378,763

4 Claims.

This invention relates to that class of rotary tools which have peripheral cutting portions adapted on rotation and axial advance of the tool nection with the accompanying drawing, where-- in by way of example I have shown a particular construction for a thread-cutting tap and where- Fig. l is a side elevation of the tap; and

Fig. 2 is a section on the line 22 of Fig. 1 on a larger scale.

In the drawing I show a tap having a shank of ordinary form with four flutes 4 defining intervening lands provided with cutting teeth 6 of any usual or suitable form. A central kerf 8 may extend between diametrically opposite flutes dividing the toothed portion of the tap into opposed sections or legs which may be spread apart by a suitable wedging action exerted at the kerf, thus to adjust the external diameter of the tap. Locking screws ll] transverse to the kerf serve to restrain and limit the expansive movement.

Taps split as described are known and various mechanisms for expanding them have been proposed. These, however, are not altogether satisfactory, particularly in the case of smaller sizes of taps wherein dimensions are small. Obviously the adjusting means must be strong and durable. At the same time if much metal is removed from the body of the tool to accommodate the adjusting means, the tap body itself is unduly weakened. The construction which I am about to describe overcomes these difliculties.

The constructiongiven the tap body in providing for the adjustment may be most simply described in terms of a preferred method of making it. Referring particularly to Fig.2, a hole l2 may be drilled in the plane of the kerf 8', in the embodiment shown transversely across the shank of the tap, and providing when the shank is kerfed opposed recesses in the walls of the kerf. The hole I2 may then be reamed to a suitable taper, as illustrated in Fig. 1, the recesses then is then tapped with a straight thread l4, that is,

a thread having equal pitch diameters through,- out, such as is formed on the usual machine screw nut, the proportion and arrangement being such that the inner diameter of the theoretical complete thread lies, at least substantially throughout the hole, inwardly of the conical surface while the outer diameter extends outwardly beyond that surface. The resultant construction might be otherwise described as that of an opening provided with a straight female thread with the inner crests of the threads cut away to correspond to the surface of a conical frustum, the elements of which (using the word elements in the geometrical sense) lie between the inner and outer cylindrical surfaces corresponding to the inner and outer diameters of the thread M.

The opening described receives an expanding element I6 in the nature of a plug, the central portion of which may be cylindrical and provided with a complete straight male thread 18 fitting the thread I4 in the hole, while the upper and lower portions 20 and 22 respectively are conical frusta tapered to correspond to the taper of the hole. The expanding member is provided with a slot 24 to receive a screw driver.

It will be apparent from Fig. 2 that, if the member I6 is inserted in the opening I2 and rotated so that the cooperating threads draw it downwardly, viewing Fig. 2, the conical portions will serve to wedge apart the legs of the tap and 7 increase the effective diameter of the latter. The screws ID are set up to clamp the legs against the expanding element and lock the legs in adjusted position.

Since the interengaging threads l4 and I8 are straight threads (as distinguished from tapered threads), they may be accurately and uniformly cut and are strong and well adapted to exert a steady and powerful force when the expanding member is rotated. The conical surfaces 20 and 22 and the thread I8 are of approximately like size, as appears in Fig. 2. Thus, on the one hand, the thread may be made of large diameter Without the necessity of removing a large amount of metal to accommodate the cone and, on the other hand, for a given size of cone the size and strength of the thread section is not scamped. A strong and durable constructtion with a, minimum loss ofmetal from the body of the tap is thus provided for.

I am aware that the invention may be embodied in other specific forms without departing from the spirit or essential atributes thereof, and I therefore desire the present embodiment to be considered in all respects as illustrative and not restrictive; reference being bad to the app nded claims rather than to the foregoing description to indicate the scope of the invention.

kerfed longitudinally to provide relatively -expansible portions and is provided with an opening substantially in the plane of the kerf having a straight thread, the crests of the thread throughout at least a portion of its extent being having a portion with a corresponding straight male thread and an unthreaded portion correspondingly tapered.

3. A rotary tool of the class described which is kerfed longitudinally to provide relatively expansible portions, an expanding member to enter the kerf having a central portion with a straight thread and end portions corresponding to frusta of a cone, the elements of which intersect the straight thread between the inner and outer diameters thereof, the walls of the kerf having recesses presenting parts of a straight female thread to fit said central thread, the inner crests of such thread being cut away to correspond to the 'an'gle'ofthe cone.

4. A tool of the class described having relatively expansible legs, a conical plug having a straight thread projecting from a portion only of its conical surface, the legs presenting recesses cut away on a taper, and an expanding member coned to fit the plug and havin cut therein a portion of a straight thread in which the thread of the'plug fits.

' CHARLES C. WINTER. 

